1. Field of the Invention
This invention relates primarily to an electrical winding or coil and the method of fabricating such a winding, and more specifically, this invention relates to the structure and method of fabrication of a superconductive winding with cooling passages formed therein.
2. Description of the Prior Art
The phenomenon of superconductivity (i.e., the exhibition of no electrical resistance by some materials when cooled to near absolute zero) has been known since 1911. In view of the very large currents and corresponding high density magnetic fields that can be achieved by utilization of superconductors, the possibilities for use of the superconductive effect in certain electromagnetic devices requiring high magnetic fields is obvious. within the last 10 or 12 years, and especially within the last 2 or 3 years, interest in utilizing superconductors in electromagnetic devices has mushroomed.
As the superconductive effect will be "quenched" or lost unless the superconductors are maintained at very low temperatures, it is imperative that adequate refrigeration or cooling arrangements be provided. Thus, when a winding or coil is formed of superconductive wires, provision must be made for bringing a coolant or refrigerant into intimate contact with the superconductors. (Of course, the benefits and advantages that may be derived from introducing a coolant to the interior of a conventional winding or coil are also clear.)
Prior art arrangements have normally involved either loosely bundled windings or tightly bundled windings having flow separators of various types. Examples of this latter type of structure may be seen in: U.S. Pat. No. 3,559,126 - Drautman, Jr.; U.S. Pat. No. 3,501,727 - Kafka; U.S. Pat. No. 3,444,307 - Kafka; U.S. Pat. No. 3,416,111 - Bogner; and U.S. Pat. No. 3,363,207 - Brechna.
In the loosely bundled winding, there might be relative motion between the individual cables or wires that form the winding. Such relative movement results in a number of deleterious effects, especially when superconductors are utilized. First of all, the relative motion of the conductors causes abrasion of the insulation that can lead to electrical failures. In addition, the motion of the individual conductors relative to the magnetic field results in electromagnetic losses. These losses result, of course, in heating that increases the amount of cryogenic refrigeration that is required. If these losses are great enough, quenching of the superconductors may result, with the subsequent loss of the magnetic field. Another cause of undesired heating in a loosely bundled winding, leading to the same deleterious effects as electromagnetic losses, is mechanical friction between the conductors. A further problem resulting from movement of the conductors is that the shape of the magnetic field may be altered with attendant disadvantages, A still further disadvantage of the loosely bundled windings is that they can become tightly packed in certain areas, leading to a "hot spot" at such a locality.
Because of the many problems associated with loosely packed windings, various attempts have been made to utilize tightly bound windings separated by some type of porous medium, generally a copper mesh. Although this type of winding is much more mechanically stable than a loosely bound winding, it also has a number of disadvantages. For one thing, the spacer occupies some volume of the winding. In addition, the spacers utilized generally have relatively low structural rigidity and thus some conductor motion may still result. Further, the use of such spacers will generally result in increases in the time and cost of producing the winding. Still further, normally only one portion of the conductors are cooled, and heat must be generally removed through a layer of electrical insulation.
The system disclosed in the above-identified Brechna patent involves a structure that is proposed to improve the cooling effect by directing the coolant around the conductors as well as through the porous medium that separates layers of the conductors. However, the Brechna arrangement still involves the other disadvantages referred to in connection with windings that utilize spacers.